In the set-up, two phase-locked frequency combs are used in a coherent linear optical sampling configuration, also known as a multi-heterodyne. What this means is that one frequency comb measures the distance path, while the other is used to read out the distance information encoded in the light of the first comb.

Pulses from one frequency comb are launched out of the fibre and hit two glass plates (a target and a reference). The plates reflect 4% of the pulse back down the fibre, effectively creating two new pulses. The time separation between the two pulses gives the distance between the target and reference plates.